Site not working when widget active

Thanks for your work on this plugin, it is fantastic.
I am having issues with my site when the widget is active on the sidebar. When I navigate to a page that has a sidebar, the page is just plain white, nothing loads. When I deactivate the widget, the site loads properly.
I am thinking this might be a CSS issue?
Any ideas how I can fix this so the widget displays?

https://wordpress.org/plugins/all-in-one-event-calendar/